Kansas City Lightning: The Rise and Times of Charlie Parker by Stanley Crouch:
Whether or not they thought about it, all good improvisers called upon those resources. But Charlie Parker wanted to be more than good; he wanted to be different. Part of your statement was your sound, and the one he was developing struck some more conventional musicians as brittle or harsh. Parker didn’t care. He didn’t want the kind of rich vibrato that characterized the sound of older players—Coleman Hawkins, Johnny Hodges—that would almost force each note in his compulsively swift phrases to seep into the next. He needed pitches that came out of the horn quicker, that were as blunt as snapping fingers when the inspiration demanded. His tone was absolutely unorthodox, as much like a snare drum or a bongo as a voice. It was assertive, at times comic or cavalier, and though often sweet, it could also sound almost devoid of pity. One trumpeter thought it sounded like knives being thrown into the audience.
When he arrived at the Woodside that night, Charlie smiled. “The sap is flowing,” he said—code for “I’m going to blow my ass off tonight.”
“Yeah, Bird,” McShann responded, “I’m sure it is.”